Move the source files into a new default directory.

src/main/java/org/nwapw/abacus/parsing/Parser.java

@@ -0,0 +1,20 @@
+package org.nwapw.abacus.parsing;
+
+import org.nwapw.abacus.tree.TreeNode;
+
+import java.util.List;
+
+/**
+ * An itnerface that provides the ability to convert a list of tokens
+ * into a parse tree.
+ * @param <T> the type of tokens accepted by this parser.
+ */
+public interface Parser<T> {
+
+    /**
+     * Constructs a tree out of the given tokens.
+     * @param tokens the tokens to construct a tree from.
+     * @return the constructed tree, or null on error.
+     */
+    public TreeNode constructTree(List<T> tokens);
+}